Coatings have been used in various industries for a wide range of metallic and non-metallic substrates. Certain coatings, particularly in the refinish industry, must be provided as two or more components that are maintained separately until just prior to application since the components will begin to react upon contact. The practice of supplying coatings as two or more separate components is common where ambient or moderate cure temperature is required. Examples include polyisocyanates and polyols, polyepoxides and polyamines, and polyanhydrides and polyols, in the Automotive Refinish Industry for example, a polyol and catalyst are typically supplied as one coating component and a polyisocyanate is supplied as the other coating component. These components are then weighed, mixed, sprayed on to an automobile and allowed to cure to form a polyurethane coating.
The two component approach presents several challenges when applying a coating. One is the need to accurately weigh each component so the reactive groups, such as the isocyanate and hydroxyl groups, are in an acceptable ratio. Another is the need to work in a timely manner so that the mixed components maintain a low enough viscosity for spraying. The span of time during which the coating is ready to apply and still of low enough viscosity to be applied is commonly referred to as “pot life.”
Typically, pot life must be balanced with cure speed of the applied coating. For instance, in a multi-component coating system that uses a catalyst, the pot life and cure speed are primarily controlled by the amount of catalyst present. Accordingly, if a fast cure speed is required more catalyst can be used but that will also cause a shorter pot life. Conversely, if a longer pot-life is needed less catalyst can be used but the cure speed would also be retarded.
It is also important that the applied coating composition dry and harden quickly so that dirt pick-up is minimized and valuable shop space isn't occupied with the coated substrate, such as an automobile, while it is drying. The length of time between when a coating is applied to a substrate and when the coating has dried or cured sufficiently that dust falling onto the coated substrate will not stick to the coated substrate is referred to as “dust-free time” and is an indicator of the speed of cure. One way to speed the drying and cure of the composition is to add additional catalyst, but this shortens the time available for spraying since higher catalyst levels also cause viscosity of the composition to increase more quickly.
Therefore, it would be desirable to have a coating system for use at ambient temperature where the pot life and cure speed may be better controlled.